One or more aspects of the inventive concept relate to power supply devices that may be used to perform charge pumping in electrical circuits. More particularly, the inventive concept relates to power supply devices capable of performing charge pumping while also preventing a latch-up phenomenon in order to stably supply an output voltage.
In general operation, a direct current (DC) voltage supply converts an alternating current (AC) voltage into a direct current (DC) voltage that may then be used to in an electronic device. One common type of DC voltage supply is the switching mode power supply (SMPS). The SMPS is highly efficient and relatively small-sized and light weight.
A DC voltage provided by the SMPS may be variously applied to system components and circuits within an electronic device. The SMPS is required to provide one or more DC voltages (e.g., 5 V, 3.3 V, and/or 12 V) within the electronic device. Accordingly, a charge pump may be incorporated to receive a (base) DC voltage from the SMPS, boost the DC voltage to an appropriate level, and then provided the boosted-level DC voltage to some circuit or component (e.g., a chip set or memory) in the electronic device.
In this regard, a Complementary Metal Oxide Semiconductor (CMOS) charge pump receives a clock signal (or phase signal) as a reference signal during operation, boosts a DC voltage using a capacitor and in response to reference signal, and then provides the boosted voltage to an output terminal via a transfer switch. Current consumption may occur via the output terminal when to an external load is connected. As the current consumption increases, the boosted voltage apparent at the output terminal may not be constantly maintained. Thus, the CMOS charge pump should be designed to supply a constant, boosted voltage regardless of current consumption at a connected output terminal.
The CMOS charge pump may use an NMOS transistor or a PMOS transistor as a transfer switch. In an NMOS type charge pump, electrical charge is only delivered at high speeds from an input direction to an output direction, but the voltage provided to the output terminal is reduced by a threshold voltage Vth of the NMOS transistor, thereby reducing output efficiency.
In contrast, a PMOS type charge pump is capable of delivering a boosted voltage to an output terminal without a threshold voltage drop. From among various PMOS type charge pumps, the so-called cross-coupled charge pump finds use in many applications. In a cross-coupled charge pump, a bulk node and an output node of a PMOS transistor are directly connected to each other, and therefore, any change in the output voltage will be mirrored by a resulting change in a bulk voltage. Thus, when leakage current flows through a bulk node of a device having a CMOS structure not only is power loss, but also a certain latch-up phenomenon may occur, thereby impairing the overall reliability of the electronic device incorporating the DC power supply.